This study aims to evaluate various methods of measuring pain relief in subjects who have chronic OA of the knee. After a 1 week of wash-out from existing therapy, subjects will be treated in a blinded fashion for 1 week with either naproxen (3 days at 250 mg twice a day followed by 4 days at 500 mg twice a day) or placebo. After the first week of treatment, subjects will have another week of wash-out followed by a second period of 1 week of the alternate treatment. Subjects will not be allowed to use oral non-steroidal anti-inflammatory drugs (NSAIDs) or other oral analgesics, or topical medications on their target knees during the study. Acetaminophen will be allowed as a rescue medication.